The disadvantage of current prior art antimicrobial packages is that the components are continuously released or are in continuous contact with the foods, also when no microorganisms are present, or are released under the influence of mechanical activity. Presence of (harmful) microorganisms, however, hardly ever involves mechanical activity, so that such a package is not usable for preventing decay of foods.
Similarly, the encapsulation of antimicrobials is known from applications in coatings, paint, cosmetics and general anti-fouling compositions, but here again the currently used vehicles mainly provide for a continuous release of the antimicrobial compound, which is not desirable for environmental reasons: such a continuous release causes an abundance of antimicrobial components in the environment which can give rise to an unwanted increased antibiotic resistance in microbial populations.
Induced release is also preferable in pharmaceutical and/or nutraceutical compositions. It enables high concentrations of active components locally, which means that the total dose to be administered can be decreased. Further, it prevents unwanted or even toxic effects to occur at sites where no medication is needed.
Several vehicles for active ingredients have already been described in the literature, especially in the field of antimicrobial active components. WO 95/17816 describes an edible pest repellent which can be encapsulated in cellulose or derivatives. The active compound is slowly released from said vehicle. GB 2198062 describes a plastic film containing microcapsules with active components, such as insect repellents. However, these capsules need mechanical pressure to release the active ingredient.
Degradable capsules have been disclosed in WO 99/08553, wherein the capsules are made of “edible polymers” such as polyvinylpyrrolidone, polyethylene wax, etc. A special form of degradable capsules is presented in WO 95/33773 in which capsules of chitine or chitosan are presented containing an active ingredient. These capsules would be degradable by lysozyme through hydrolysis. GB 1576999 describes the use of biopolymers, which are coagulated at elevated temperature (120° C.) in “vasiline petroleum gelly” and contain either organic tin compounds or Cu2O. These particles are used as additive in anti fouling paint. The disadvantage of the described system is that for instance heat sensitive and/or organic solvent sensitive active ingredients cannot be used and also the formed capsules cannot be filled with an active ingredient once the vehicle is formed.
Thus, there is still need for alternative vehicles encapsulating an active ingredient which would be able to release their content on demand, i.e. at a specified place and/or time, due to an external (physical, chemical or enzymatical) trigger or stimulus.